Methods of bonding semiconductor elements to a substrate, including use of a reducing gas, and related bonding machines

ABSTRACT

A method of bonding a semiconductor element to a substrate includes: carrying a semiconductor element including a plurality of first electrically conductive structures with a bonding tool; supporting a substrate including a plurality of second electrically conductive structures with a support structure; providing a reducing gas in contact with each of the plurality of first conductive structures and the plurality of second conductive structures; establishing contact between corresponding ones of the plurality of first conductive structures and the plurality of second conductive structures; moving at least one of the semiconductor element and the substrate such that the corresponding ones of the plurality of first conductive structures and the plurality of second conductive structures are separated; re-establishing contact between the plurality of first conductive structures and the plurality of second conductive structures; and bonding the plurality of first conductive structures to the respective ones of the plurality of second conductive structures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/630,619, filed Feb. 14, 2018, and of U.S. Provisional Application No.62/790,200, filed Jan. 9, 2019, the contents of both of which areincorporated herein by reference.

FIELD

The invention relates to bonding processes (such as flip chip and/orthermocompression bonding processes) and bonding machines (such as flipchip and/or thermocompression bonding systems), and more particularly,to improved methods of bonding a semiconductor element to a substrateincluding the use of a reducing gas.

BACKGROUND

Traditional semiconductor packaging typically involves die attachprocesses and wire bonding processes. Advanced semiconductor packagingtechnologies (e.g., flip chip bonding, thermocompression bonding, etc.)technologies continue to gain traction in the industry. For example, inthermocompression bonding (i.e., TCB), heat and/or pressure (andsometimes ultrasonic energy) are used to form a plurality ofinterconnections between (i) electrically conductive structures on asemiconductor element and (ii) electrically conductive structures on asubstrate.

In certain flip chip bonding or thermocompression bonding applications,the electrically conductive structures of the semiconductor elementand/or the substrate may include copper structures (e.g., copperpillars) or other material(s) that is subject to oxidation and/or othercontamination. In such applications, it is desirable to provide anenvironment suitable for bonding. Conventionally, such an environmentmay be provided by using a reducing gas at the bonding area to reducepotential oxidation and/or contamination of the electrically conductivestructures of the semiconductor element or the substrate to which itwill be bonded.

Thus, it would be desirable to provide improved methods of bondingsemiconductor elements to a substrate with the use of a reducing gas.

SUMMARY

According to an exemplary embodiment of the invention, a method ofbonding a semiconductor element to a substrate is provided. The methodincludes the steps of: (a) carrying a semiconductor element with abonding tool of a bonding machine, the semiconductor element including aplurality of first electrically conductive structures; (b) supporting asubstrate with a support structure of the bonding machine, the substrateincluding a plurality of second electrically conductive structures; (c)providing a reducing gas in contact with each of the plurality of firstelectrically conductive structures and the plurality of secondelectrically conductive structures; (d) establishing contact betweencorresponding ones of the plurality of first electrically conductivestructures and the plurality of second electrically conductivestructures after step (c); (e) moving at least one of the semiconductorelement and the substrate after step (d) such that the correspondingones of the plurality of first electrically conductive structures andthe plurality of second electrically conductive structures are separatedfrom one another; (f) re-establishing contact between the correspondingones of the plurality of first electrically conductive structures andthe plurality of second electrically conductive structures after step(e); and (g) bonding the corresponding ones of the plurality of firstelectrically conductive structures to the respective ones of theplurality of second electrically conductive structures after step (f).

According to another exemplary embodiment of the invention, a bondingmachine for bonding a semiconductor element to a substrate is provided.The bonding machine includes a bond head including a bonding tool, thebonding tool being configured to carry a semiconductor element, thesemiconductor element including a plurality of first electricallyconductive structures. The bonding machine also includes a supportstructure for supporting a substrate, the substrate including aplurality of second electrically conductive structures. The bondingmachine also includes a manifold for directing a reducing gas to contacteach of the plurality of first electrically conductive structures andthe plurality of second electrically conductive structures. Prior tobonding of corresponding ones of the plurality of first electricallyconductive structures to the respective ones of the plurality of secondelectrically conductive structures, the bonding machine is configured to(i) establish contact between the corresponding ones of the plurality offirst electrically conductive structures and the plurality of secondelectrically conductive structures, (ii) move at least one of thesemiconductor element and the substrate after step (i) such that thecorresponding ones of the plurality of first electrically conductivestructures and the plurality of second electrically conductivestructures are separated from one another, and (iii) re-establishcontact between the corresponding ones of the plurality of firstelectrically conductive structures and the plurality of secondelectrically conductive structures after step (ii). For example, such abonding machine may be configured to perform steps (i), (ii), and (iii)by following computer program instructions included on a computer of thebonding machine (e.g., any one of bonding machines 100, 100′, 100″, and100′″ illustrated in the drawings and described herein).

According to yet another exemplary embodiment of the invention, a methodof bonding a semiconductor element to a substrate is provided. Themethod includes the steps of: (a) carrying a semiconductor element witha bonding tool of a bonding machine, the semiconductor element includinga plurality of first electrically conductive structures; (b) supportinga substrate with a support structure of the bonding machine, thesubstrate including a plurality of second electrically conductivestructures; (c) providing a reducing gas in contact with each of theplurality of first electrically conductive structures and the pluralityof second electrically conductive structures, the reducing gas beingprovided via a manifold for directing the reducing gas to contact eachof the plurality of first electrically conductive structures and theplurality of second electrically conductive structures, the manifoldincluding a fluid channel for carrying the reducing gas, the fluidchannel being provided along an angle with respect to a horizontal planeof the bonding machine, the angle being between 10-60 degrees; and (d)bonding the corresponding ones of the plurality of first electricallyconductive structures to the respective ones of the plurality of secondelectrically conductive structures after step (c).

According to yet another exemplary embodiment of the invention, abonding machine for bonding a semiconductor element to a substrate isprovided. The bonding machine includes a bond head including a bondingtool. The bonding tool is configured to carry a semiconductor element.The semiconductor element includes a plurality of first electricallyconductive structures. The bonding machine also includes a supportstructure for supporting a substrate. The substrate includes a pluralityof second electrically conductive structures. The bonding machine alsoincludes a manifold for directing a reducing gas to contact each of theplurality of first electrically conductive structures and the pluralityof second electrically conductive structures. The manifold includes afluid channel for carrying the reducing gas, the fluid channel beingprovided along an angle with respect to a horizontal plane of thebonding machine, the angle being between 10-60 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. It is emphasizedthat, according to common practice, the various features of the drawingsare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawings are the following figures:

FIGS. 1A-1I are a series of block diagram illustrations of a bondingmachine in accordance with an exemplary embodiment of the invention,also illustrating a method of bonding a semiconductor element to asubstrate in accordance with an exemplary embodiment of the invention;

FIG. 2A is a block diagram illustration of another bonding machine inaccordance with another exemplary embodiment of the invention;

FIG. 2B is detailed view of a portion of the bonding machine of FIG. 2A;

FIGS. 3A-3I are a series of block diagram illustrations of a bondingmachine in accordance with another exemplary embodiment of theinvention, also illustrating another method of bonding a semiconductorelement to a substrate in accordance with an exemplary embodiment of theinvention;

FIG. 4A is a block diagram illustration of yet another bonding machinein accordance with another exemplary embodiment of the invention; and

FIG. 4B is detailed view of a portion of the bonding machine of FIG. 4A.

DETAILED DESCRIPTION

As used herein, the term “semiconductor element” is intended to refer toany structure including (or configured to include at a later step) asemiconductor chip or die. Exemplary semiconductor elements include abare semiconductor die, a semiconductor die on a substrate (e.g., aleadframe, a PCB, a carrier, a semiconductor chip, a semiconductorwafer, a BGA substrate, a semiconductor element, etc.), a packagedsemiconductor device, a flip chip semiconductor device, a die embeddedin a substrate, a stack of semiconductor die, amongst others. Further,the semiconductor element may include an element configured to be bondedor otherwise included in a semiconductor package (e.g., a spacer to bebonded in a stacked die configuration, a substrate, etc.).

As used herein, the term “substrate” is intended to refer to anystructure to which a semiconductor element may be bonded. Exemplarysubstrates include, for example, a leadframe, a PCB, a carrier, amodule, a semiconductor chip, a semiconductor wafer, a BGA substrate,another semiconductor element, etc.

Aspects of the invention may have particular applicability in connectionwith electrically conductive structures of a semiconductor elementincluding copper, and when such electrically conductive structures arebonded (e.g., thermocompressively bonded) to electrically conductivestructures of a substrate that also include copper, and further wherethe bonding occurs in the presence of a reducing gas. Using heat (e.g.,from the heater of the bond head assembly) provided through the bondingtool, and the reducing gas, oxides and/or other contaminants on thesurface of the electrically conductive structures (of the semiconductorelement and/or the substrate) may be cleaned. Such a cleaning techniquehas been found to have particular applicability in copper to copperthermocompression bonding, where the electrically conductive structureson the semiconductor element (and/or the substrate) may be copperpillars, other copper structures, other conductive structures includingcopper, or the like.

In accordance with exemplary aspects of the invention, methods ofbonding semiconductor elements are provided (in the presence of areducing gas, such as a formic acid vapor) during which heat provided bya heater in the bond head assembly is transferred from (a) ones ofelectrically conductive structures of a semiconductor element to (b)respective ones of electrically conductive structures of the substrateto which the semiconductor element is being bonded. In particular, it isdesirable that a portion of the electrically conductive structures ofthe substrate are adequately heated for cleaning—because surfaces of theelectrically conductive structures of the substrate will be later usedin connection with the bonding process.

In specific examples of such methods, a semiconductor element (e.g., asemiconductor chip) is transferred from a source (e.g., a semiconductorwafer) to a bonding tool of a thermocompression bonding machine or aflip chip bonding machine. With the semiconductor element carried by thebonding tool (e.g., using vacuum), the bond head assembly (carrying thebonding tool) is moved to a desired bonding position.

At the bonding position, contact is made between (i) ones of theelectrically conductive structures of the semiconductor element and (ii)respective ones of the electrically conductive structures of thesubstrate. At this contact, force may be applied by the bonding tool(via the semiconductor element) in a range of, for example, 1-10 N, 5-10N, among other ranges. An exemplary temperature range of thesemiconductor element is between 300-400° C., while a correspondingexemplary temperature range at the interface of the electricallyconductive structures of the semiconductor element after contact withthe respective electrically conductive structures of the substrate is200-250° C. Such an interface temperature may be adequate, depending onthe application, for provoking the desired reaction for cleaning theelectrically conductive structures of the substrate.

Localized heating provided to the electrically conductive structures ofthe semiconductor element (and the electrically conductive structures ofthe substrate), in the presence of the reducing gas (e.g., formic acidvapor) assists to clean the copper oxides on surfaces of theelectrically conductive structures, especially at the interface regionbetween the corresponding electrically conductive structures to bejoined through the bonding process. The localized heating may beprovided, at least in part, by contact between the correspondingelectrically conductive structures to be joined. This contact step(which, as explained herein, includes separation of the correspondingelectrically conductive structures after contact such as shown in FIG.1E, explained below) may be repeated as desired, in connection with thereducing gas in the bonding area, until an acceptable amount of oxideand/or other contamination is removed. The duration of the contact step(or the separation between contact), and the number of contactrepetitions, may be determined by application specific factors such asthe thickness of the oxide (or other contaminants) on the electricallyconductive structures on the substrate (and/or the electricallyconductive structures of the semiconductor element). A key advantage ofthis method is the potential to avoid excessive heating of the substrateat a high temperature (e.g., substrate 104 may be at a temperaturebetween 70° C.-100° C. during the method shown in FIGS. 1A-1I),especially for large substrate sizes (e.g., Ø=300 mm).

Other localized heating methods, such as laser assisted heating of atarget area on the substrate (e.g., an interface region of theelectrically conductive structures of the substrate), are contemplated.For example, such laser assisted heating may involve a raster scanfashion to target the entire bonding area.

Throughout the various drawings, like reference numerals refer to thelike elements, except where explained herein.

Referring now to the drawings, FIG. 1A illustrates bonding machine 100(e.g., a flip chip bonding machine, a thermocompression bonding machine,etc.). Bonding machine 100 includes a support structure 102 forsupporting a substrate 104 during a bonding operation (where substrate104 includes a plurality of electrically conductive structures 104 a).Support structure 102 may include any appropriate structure for thespecific application. In FIGS. 1A-1I, support structure 102 includes topplate 102 a (configured to directly support substrate 104), chuck 102 c,and heater 102 b disposed therebetween. In applications where heat forheating substrate 104 is desirable in connection with the bondingoperation, a heater such as heater 102 b may be utilized.

FIG. 1A also illustrates bond head assembly 106, which may be configuredto move along (and about) a plurality of axes of bonding machine 100such as, for example, the x-axis, y-axis, z-axis, theta (rotative) axis,etc. Bond head assembly 106 includes heater 108 and bonding tool 110.That is, in certain bonding machines (e.g., thermocompression bondingmachines) it may be desirable to heat the bonding tool. Thus, while FIG.1A illustrates a separate heater 108 for heating bonding tool 110 (forheating semiconductor element 112 including a plurality of electricallyconductive structures 112 a), it will be appreciated that heater 108 andbonding tool 110 may be integrated into a single element (e.g., a heatedbonding tool).

In connection with a bonding operation, semiconductor element 112 isbonded to substrate 104 using bonding tool 110. During the bondingoperation, corresponding ones of electrically conductive structures 112a are bonded (e.g., using heat, force, ultrasonic energy, etc.) torespective ones of electrically conductive structures 104 a.

In certain bonding applications (e.g., flip chip and/orthermocompression bonding with copper conductive structures), it isdesirable to provide an environment suitable for bonding.Conventionally, such an environment may be provided by using a reducinggas at the bonding area to reduce potential contamination of theelectrically conductive structures of the semiconductor element or thesubstrate to which it will be bonded.

In FIG. 1A, bond head assembly 106 carries a bond head manifold 114 forreceiving and distributing fluids (e.g., gases, vapors, etc.) as desiredin the given application. In FIG. 1A, while bond head manifold 114 isillustrated in a cross sectional view, the actual bond head manifold 114surrounds bonding tool 110 (e.g., bond head manifold 114 surroundsbonding tool 110 in a coaxial configuration). Of course, bond headmanifold 114 may have different configurations from that shown in FIG.1A. Further, it is understood that certain details of bond head manifold114 (e.g., interconnection with piping 120, structural details fordistributing a reducing gas within bond head manifold 114, structuraldetails for distributing a shielding gas within bond head manifold 114,structural details for drawing a vacuum through a center channel of bondhead manifold 114, etc.) are omitted for simplicity.

Bond head manifold 114 includes three channels 114 a, 114 b, 114 chaving different functions. Outer channel 114 a receives a shielding gas(e.g., nitrogen gas) from shielding gas supply 118. That is, a shieldinggas is provided from shielding gas supply 118 (e.g., a nitrogen supply),through piping 120 (where piping 120 may include hard piping, flexibletubing, a combination of both, or any other structure adapted to carrythe fluids described herein), to outer channel 114 a of bond headmanifold 114. From outer channel 114 a of bond head manifold 114, theshielding gas 128 is provided as a shield from the outside environment(e.g., see FIG. 1C).

Inner channel 114 c receives a reducing gas 130 (e.g., see FIG. 1C)(e.g., where the reducing gas is a saturated vapor gas) via piping 120,and provides reducing gas 130 in the area of semiconductor element 112and substrate 104 in connection with a bonding operation. Reducing gas130 is provided by a vapor generation system 122, but initiates asreducing gas 126. In the example shown in FIG. 1A, vapor generationsystem 122 is a bubbler type system including an acid fluid 124 (e.g.,formic acid, acetic acid, etc.) in vessel 122 a of the bubbler typesystem. A carrier gas (e.g., nitrogen) is provided (via piping 120) intoacid fluid 124 in vessel 122 a, where the carrier gas acts as a carrierfor the acid fluid 124. Collectively, the carrier gas (e.g., nitrogen)and acid fluid 124 are transported as reducing gas 126. Within piping120, additional carrier gas (e.g., nitrogen) may be added to reducinggas 126 (e.g., to vary the concentration of the reducing gas, asdesired) via piping section 120 a, thereby providing reducing gas 130 inthe area of semiconductor element 112 and substrate 104 in connectionwith the bonding operation. After reducing gas 130 is distributed in thearea of semiconductor element 112 and substrate 104, reducing gas 130contacts surfaces of each of electrically conductive structures 104 aand electrically conductive structures 112 a. The surfaces ofelectrically conductive structures 104 a/112 a may then include areaction product (e.g., where the reaction product is provided as aresult of (i) a surface oxide on electrically conductive structures 104a/112 a, (ii) reducing gas from reducing gas 130, and (iii) heatprovided by heater 108 and transferred to electrically conductivestructures 104 a via contact with electrically conductive structures 112a that were already heated). This reaction product is desirably removedfrom the bonding area (i.e., the area where electrically conductivestructures 112 a of semiconductor element 112 are bonded tocorresponding electrically conductive structures 104 a of substrate 104)using vacuum provided through center channel 114 b of bond head manifold114 via exit piping 116.

Thus, FIG. 1A illustrates: (i) various elements of bonding machine 100;(ii) a path of carrier gas from carrier gas supply 118 to outer channel114 a of bond head manifold 114; (iii) a path of reducing gas 126 (whichmay receive additional carrier gas from piping 120) from vaporgeneration system 122 to inner channel 114 c of bond head manifold 114,where it is released to the bonding area as reducing gas 130; and (iv) apath of gas (which may carry away a reaction product from surfaces ofelectrically conductive structures 104 a/112 a) drawn by vacuum throughcenter channel 114 b of bond head manifold 114. The aforementioned pathsare illustrated in FIG. 1A through various arrows even though gas is notflowing in FIG. 1A.

Prior to the process shown and described in connection with FIGS. 1A-1I,semiconductor element 112 and/or substrate 104 may be “cleaned”. Forexample, the electrically conductive structures 112 a, 104 a of one orboth of semiconductor element 112 and substrate 104 may be cleaned usinga solution such as hydrochloric acid or acetic acid. Such a cleaningstep may be performed, for example, by dipping at least a portion ofsemiconductor element 112 and/or substrate 104 into such a solution.

At FIG. 1B, bond head assembly 106 has been lowered from the positionshown in FIG. 1A (as indicated by the downward arrow on the right handside of the drawing) such that an initial touchdown is establishedbetween ones of electrically conductive structures 112 a and respectiveones of electrically conductive structures 104 a. Such an initialtouchdown may be useful for establishing a z-axis position (e.g., aheight) of the initial contact between conductive structures 112 a andcorresponding conductive structures 104 a for use during bonding. Afterthe initial touchdown in FIG. 1B, vapor generation system 122 isactivated to produce reducing gas 130 at the bonding area (e.g., seeFIG. 1C).

FIG. 1C illustrates reducing gas 130 being provided at the bonding area,as well as shielding gas 128 being provided, and vacuum being drawnthrough center channel 114 b of bond head manifold 114 via exit piping116. At FIG. 1C, bond head assembly 106 has been raised (as indicated bythe upward arrow on the right hand side of the drawing) (e.g., by apredetermined distance to allow the flow of reducing gas 130 to reachdesired portions of semiconductor element 112 and substrate 104) suchthat the corresponding electrically conductive structures 104 a andelectrically conductive structures 112 a are separated from one another.At FIG. 1C, heater 108 has heated semiconductor element 112 (andelectrically conductive structures 112 a) to a temperature (e.g., atemperature in the range of 300-400° C., a temperature in the range of350-400° C., etc.). With reducing gas 130, and the heat provided toelectrically conductive structures 112 a by heater 108, electricallyconductive structures 112 a may be considered as “clean”. That is,contaminants (e.g., a surface oxide) on the surface of electricallyconductive structures 112 a react with reducing gas 130 and heat to forma reaction product that is desirably removed from the bonding area usingvacuum provided through center channel 114 b of bond head manifold 114.

At FIG. 1D, bond head assembly 106 has been lowered to the same positionas in FIG. 1B (as indicated by the downward arrow on the right hand sideof the drawing) such that touchdown is re-established between ones ofelectrically conductive structures 104 a and respective ones ofelectrically conductive structures 112 a. A bond force (e.g., 1-10 N,5-10 N, less than 10 N, etc.) may be applied by bond head assembly 106carrying bonding tool 110. The contact between electrically conductivestructures 104 a and respective electrically conductive structures 112 aat this step may be for any duration in order to provide the desiredheat transfer. That is, heat transfer occurs at this step, becauseelectrically conductive structures 112 a have been heated by heater 108(e.g., to a temperature between 300-400° C.), and heat transfers toelectrically conductive structures 104 a. This heat provided toelectrically conductive structures 104 a, in addition to reducing gas130 adhering to surfaces of electrically conductive structures 104 a,may react with contaminants (e.g., a surface oxide) on the surfaces ofelectrically conductive structures 104 a, resulting in a reactionproduct desirably removed from the bonding area using vacuum providedthrough center channel 114 b of bond head manifold 114. This cleaningmay be continued through subsequent steps. Further, reducing gas 130 maycontinue to flow to prevent oxidation and/or other contamination onelectrically conductive structures 112 a/104 a.

At FIG. 1E, bond head assembly 106 has been raised (as indicated by theupward arrow on the right hand side of the drawing) such thatelectrically conductive structures 104 a and respective electricallyconductive structures 112 a are separated from one another. As reducinggas 130 continues to flow, the potential for further contamination maybe substantially reduced, and cleaning may continue. This step may lastany desired duration (e.g., 1-2 seconds), for example, such that thereis adequate time to remove the reaction products (e.g., oxides and/orcontamination) using the vacuum provided through center channel 114 b ofbond head manifold 114.

After FIG. 1E, the process may proceed to a bonding step (e.g., athermocompression bonding step as shown in FIG. 1H); however, additionalheat transfer (and associated cleaning) might be desired. Thus, FIGS.1F-1G might be skipped, and the process may proceed from FIG. 1E to thebonding at FIG. 1H. However, the steps shown in FIGS. 1F-1G may occur,and in fact, may be repeated a number of times if desired to continueheat transfer and cleaning through the reaction of oxides/contaminants,reducing gas 130, and heat—with the reaction product desirably beingremoved by the vacuum in center channel 114 b of bond head manifold 114.

At FIG. 1F, bond head assembly 106 has been lowered to the same positionas in FIG. 1B and FIG. 1D (as indicated by the downward arrow on theright hand side of the drawing) such that touchdown is re-established toprovide additional heat transfer from ones of electrically conductivestructures 112 a to respective ones of electrically conductivestructures 104 a.

At FIG. 1G, bond head assembly 106 has been raised (as indicated by theupward arrow on the right hand side of the drawing) such that thecorresponding electrically conductive structures 104 a and respectiveelectrically conductive structures 112 a are separated from one another.After the step shown at FIG. 1G, it may be determined that the cleaningprocess has been completed, and that the bonding process may now becompleted; however, it is understood that the steps shown at FIGS. 1F-1Gmay be repeated, as desired.

At FIG. 1H, electrically conductive structures 112 a are bonded tocorresponding electrically conductive structures 104 a. This may bethrough a thermocompression bonding process (e.g., including heat and/orbond force, where the bond force may be a higher bond force such as50-300 N), and may also include ultrasonic energy transfer (e.g., froman ultrasonic transducer included in bond head assembly 106). At FIG.1I, the bonding process has been completed. That is, semiconductorelement 112 has been bonded to substrate 104, such that correspondingelectrically conductive structures 112 a, 104 a are now bonded to oneanother.

FIGS. 2A-2B illustrate a bonding machine 100′ that is substantiallysimilar to bonding machine 100 (e.g., a flip chip bonding machine, athermocompression bonding machine, etc.) illustrated and described abovein connection with FIGS. 1A-1I. As such, for brevity, certain detailsregarding FIGS. 2A-2B are omitted from this description. Nonetheless, itis understood that the process of FIGS. 1A-1I may also be performedusing bonding machine 100′ of FIGS. 2A-2B. Bonding machine 100′ of FIGS.2A-2B differs from bonding machine 100 (of FIGS. 1A-1I) in connectionwith the inner channel of the bond head manifold. More specifically, inFIGS. 2A-2B, an inner channel 114 c′ of bond head manifold 114′ isoriented along a non-vertical path. That is, inner channel 114 c′ isangled with respect to the illustrated horizontal plane “P” (see FIG.2B). As will be appreciated by those skilled in the art, horizontalplane “P” may be oriented, for example, with respect to an x-axis and/ora y-axis of bonding machine 100′. An exemplary range for the angle “A”shown in FIG. 2B is between 10-60 degrees. By orienting inner channel114 c′ along such an angle, the reducing gas (e.g., a saturated vaporgas) may be provided more efficiently to the area of semiconductorelement 112 and substrate 104.

Although FIGS. 1A-1I illustrate manifold 114, integrated with the bondhead, for: delivering the reducing gas; delivering the shielding gas;and providing vacuum—the invention is not limited thereto. For example,instead of such functions being provided through integration of amanifold with the bond head assembly, such functions may be providedthrough integration with a support structure for supporting thesubstrate. Further, such functions may be split between the bond headassembly and the support structure (and possibly other structures of thebonding machine). FIGS. 3A-3I are a series of block diagrams of abonding machine 100″, with certain similar elements and functions tothat illustrated and described with respect to FIGS. 1A-1I, except thatthe manifold functions (delivering the reducing gas; delivering theshielding gas; and providing vacuum) are integrated into a supportstructure 202.

FIG. 3A illustrates bonding machine 100″ (e.g., a flip chip bondingmachine, a thermocompression bonding machine, etc.). Bonding machine100″ includes a support structure 202 for supporting a substrate 104during a bonding operation (where substrate 104 includes a plurality ofelectrically conductive structures 104 a). Support structure 202 mayinclude any appropriate structure for the specific application. In FIGS.3A-3I, support structure 202 includes top plate 202 a (configured todirectly support substrate 104), chuck 202 c, and heater 202 b disposedtherebetween. In applications where heat for heating substrate 104 isdesirable in connection with the bonding operation, a heater such asheater 202 b may be utilized.

FIG. 3A also illustrates bond head assembly 106 (including heater 108and bonding tool 110), which may be configured to move along (and about)a plurality of axes of bonding machine 100″ such as, for example, thex-axis, y-axis, z-axis, theta (rotative) axis, etc. In FIG. 3A, bondhead assembly 106 carries a plate 107 for partially containing at leastone of shielding gas 128 and reducing gas 130 (see description below).

As opposed to a bond head manifold 114 carried by bond head assembly 106(as in FIGS. 1A-1I), FIGS. 3A-3I illustrate a manifold 214 carried by,and/or intergrated with, support structure 202. Manifold 214 isconfigured for receiving and distributing fluids (e.g., gases, vapors,etc.) as desired in the given application. In FIG. 3A, while manifold214 is illustrated in a cross sectional view, the actual manifold 214 atleast partially surrounds substrate 104. Of course, manifold 214 mayhave different configurations from that shown in FIG. 3A. Further, it isunderstood that certain details of manifold 214 (e.g., interconnectionwith piping 120, structural details for distributing reducing gas 130within manifold 214, structural details for distributing shielding gas128 within manifold 214, structural details for drawing a vacuum througha center channel of manifold 214, etc.) are omitted for simplicity.

Manifold 214 includes three channels 214 a, 214 b, 214 c havingdifferent functions. Outer channel 214 a receives shielding gas 128(e.g., nitrogen gas) from shielding gas supply 118 via piping 120. Fromouter channel 214 a of manifold 214, shielding gas 128 is provided as ashield from the outside environment (e.g., see FIG. 3C). Inner channel214 c receives a reducing gas 130 (e.g., see FIG. 3C) (e.g., where thereducing gas is a saturated vapor gas) via piping 120, and providesreducing gas 130 in the area of semiconductor element 112 and substrate104 in connection with a bonding operation. Reducing gas 130 is providedby a vapor generation system 122, but initiates as reducing gas 126(e.g., see description above with respect to FIGS. 1A-1I). Afterreducing gas 130 is distributed in the area of semiconductor element 112and substrate 104, reducing gas 130 contacts surfaces of each ofelectrically conductive structures 104 a and electrically conductivestructures 112 a. The surfaces of electrically conductive structures 104a/112 a may then include a reaction product (e.g., where the reactionproduct is provided as a result of (i) a surface oxide on electricallyconductive structures 104 a/112 a, (ii) reducing gas from reducing gas130, and (iii) heat provided by heater 108 and transferred toelectrically conductive structures 104 a via contact with electricallyconductive structures 112 a that were already heated). This reactionproduct is desirably removed from the bonding area (i.e., the area whereelectrically conductive structures 112 a of semiconductor element 112are bonded to corresponding electrically conductive structures 104 a ofsubstrate 104) using vacuum provided through center channel 214 b ofmanifold 214 via exit piping 216.

Thus, FIG. 3A illustrates: (i) various elements of bonding machine 100″;(ii) a path of carrier gas from carrier gas supply 118 to outer channel214 a of manifold 214; (iii) a path of reducing gas 126 (which mayreceive additional carrier gas from piping 120 a) from vapor generationsystem 122 to inner channel 214 c of manifold 214, where it is releasedto the bonding area as reducing gas 130; and (iv) a path of gas (whichmay carry away a reaction product from surfaces of electricallyconductive structures 104 a/112 a) drawn by vacuum through centerchannel 214 b of manifold 214. The aforementioned paths are illustratedin FIG. 3A through various arrows even though gas is not flowing in FIG.3A.

Prior to the process shown and described in connection with FIGS. 3A-3I,semiconductor element 112 and/or substrate 104 may be “cleaned”. Forexample, the electrically conductive structures 112 a, 104 a of one orboth of semiconductor element 112 and substrate 104 may be cleaned usinga solution such as hydrochloric acid or acetic acid. Such a cleaningstep may be performed, for example, by dipping at least a portion ofsemiconductor element 112 and/or substrate 104 into such a solution.

At FIG. 3B, bond head assembly 106 has been lowered from the positionshown in FIG. 3A (as indicated by the downward arrow on the right handside of the drawing) such that an initial touchdown is establishedbetween ones of electrically conductive structures 112 a and respectiveones of electrically conductive structures 104 a. Such an initialtouchdown may be useful for establishing a z-axis position (e.g., aheight) of the initial contact between conductive structures 112 a andcorresponding conductive structures 104 a for use during bonding. Afterthe initial touchdown in FIG. 3B, vapor generation system 122 isactivated to produce reducing gas 130 at the bonding area (e.g., seeFIG. 3C).

FIG. 3C illustrates reducing gas 130 being provided at the bonding area,as well as shielding gas 128 being provided, and vacuum being drawnthrough center channel 214 b of manifold 214 via exit piping 216. Plate107 acts as a partial barrier, to partially contain (and/or slow downthe flow of) shielding gas 128 and/or reducing gas 130. At FIG. 3C, bondhead assembly 106 has been raised (as indicated by the upward arrow onthe right hand side of the drawing) (e.g., by a predetermined distanceto allow the flow of reducing gas 130 to reach desired portions ofsemiconductor element 112 and substrate 104) such that the correspondingelectrically conductive structures 104 a and electrically conductivestructures 112 a are separated from one another. At FIG. 3C, heater 108has heated semiconductor element 112 (and electrically conductivestructures 112 a) to a temperature (e.g., a temperature in the range of300-400° C., a temperature in the range of 350-400° C., etc.). Withreducing gas 130, and the heat provided to electrically conductivestructures 112 a by heater 108, electrically conductive structures 112 amay be considered as “clean”. That is, contaminants (e.g., a surfaceoxide) on the surface of electrically conductive structures 112 a reactwith reducing gas 130 and heat to form a reaction product that isdesirably removed from the bonding area using vacuum provided throughcenter channel 214 b of manifold 214.

At FIG. 3D, bond head assembly 106 has been lowered to the same positionas in FIG. 3B (as indicated by the downward arrow on the right hand sideof the drawing) such that touchdown is re-established between ones ofelectrically conductive structures 104 a and respective ones ofelectrically conductive structures 112 a. A bond force (e.g., 1-10 N,5-10 N, less than 10 N, etc.) may be applied by bond head assembly 106carrying bonding tool 110. The contact between electrically conductivestructures 104 a and respective electrically conductive structures 112 aat this step may be for any duration in order to provide the desiredheat transfer. That is, heat transfer occurs at this step, becauseelectrically conductive structures 112 a have been heated by heater 108(e.g., to a temperature between 300-400° C.), and heat transfers torespective electrically conductive structures 104 a. This heat providedto electrically conductive structures 104 a, in addition to reducing gas130 adhering to surfaces of electrically conductive structures 104 a,may react with contaminants (e.g., a surface oxide) on the surfaces ofelectrically conductive structures 104 a, resulting in a reactionproduct desirably removed from the bonding area using vacuum providedthrough center channel 214 b of manifold 214. This cleaning may becontinued through subsequent steps. Further, reducing gas 130 maycontinue to flow to prevent oxidation and/or other contamination onelectrically conductive structures 112 a/104 a.

At FIG. 3E, bond head assembly 106 has been raised (as indicated by theupward arrow on the right hand side of the drawing) such thatelectrically conductive structures 104 a and respective electricallyconductive structures 112 a are separated from one another. As reducinggas 130 continues to flow, the potential for further contamination maybe substantially reduced, and cleaning may continue. This step may lastany desired duration (e.g., 1-2 seconds), for example, such that thereis adequate time to remove the reaction products (e.g., oxides and/orcontamination) using the vacuum provided through center channel 214 b ofmanifold 214.

After FIG. 3E, the process may proceed to a bonding step (e.g., athermocompression bonding step as shown in FIG. 3H); however, additionalheat transfer (and associated cleaning) might be desired. Thus, FIGS.3F-3G might be skipped, and the process may proceed from FIG. 3E to thebonding at FIG. 3H. However, the steps shown in FIGS. 3F-3G may occur,and in fact, may be repeated a number of times if desired to continueheat transfer and cleaning through the reaction of oxides/contaminants,reducing gas 130, and heat—with the reaction product desirably beingremoved by the vacuum in center channel 214 b of manifold 214.

At FIG. 3F, bond head assembly 106 has been lowered to the same positionas in FIG. 3B and FIG. 3D (as indicated by the downward arrow on theright hand side of the drawing) such that touchdown is re-established toprovide additional heat transfer from ones of electrically conductivestructures 112 a to respective ones of electrically conductivestructures 104 a.

At FIG. 3G, bond head assembly 106 has been raised (as indicated by theupward arrow on the right hand side of the drawing) such that thecorresponding electrically conductive structures 104 a and respectiveelectrically conductive structures 112 a are separated from one another.After the step shown at FIG. 3G, it may be determined that the cleaningprocess has been completed, and that the bonding process may now becompleted; however, it is understood that the steps shown at FIGS. 3F-3Gmay be repeated, as desired.

At FIG. 3H, electrically conductive structures 112 a are bonded tocorresponding electrically conductive structures 104 a. This may bethrough a thermocompression bonding process (e.g., including heat and/orbond force, where the bond force may be a higher bond force such as50-300 N), and may also include ultrasonic energy transfer (e.g., froman ultrasonic transducer included in bond head assembly 106). At FIG.3I, the bonding process has been completed. That is, semiconductorelement 112 has been bonded to substrate 104, such that correspondingelectrically conductive structures 112 a, 104 a are now bonded to oneanother.

FIGS. 4A-4B illustrate a bonding machine 100′″ that is substantiallysimilar to bonding machine 100″ (e.g., a flip chip bonding machine, athermocompression bonding machine, etc.) illustrated and described abovein connection with FIGS. 3A-3I. Nonetheless, it is understood that theprocess of FIGS. 3A-3I may also be performed using bonding machine 100′″of FIGS. 4A-4B. Bonding machine 100′″ of FIGS. 4A-4B differs frombonding machine 100″ (of FIGS. 3A-3I) in connection with the innerchannel of the manifold. More specifically, in FIGS. 4A-4B, an innerchannel 214 c′ of manifold 214′ is oriented along a non-vertical path.That is, inner channel 214 c′ is angled with respect to the illustratedhorizontal plane “P” (see FIG. 4B). As will be appreciated by thoseskilled in the art, horizontal plane “P” may be oriented, for example,with respect to an x-axis and/or a y-axis of bonding machine 100′″. Anexemplary range for the angle “A” shown in FIG. 4B is between 10-60degrees. By orienting inner channel 214 c′ along such an angle, thereducing gas (e.g., a saturated vapor gas) may be provided moreefficiently to the area of semiconductor element 112 and substrate 104.

Although the invention has been illustrated primarily with respect toone of manifolds 114, 114′, 214, and 214′ for directing (i) the flow ofreducing gas 130, (ii) the flow of shielding gas 128, and (iii) the pullof the vacuum, it is understood that the structure used to direct theflow patterns may be different from that illustrated. That is, theconfiguration of the structure used to provide and direct fluids 130,128 (and to draw vacuum) may vary considerably from that shown.

Although the invention has been illustrated and described primarily withrespect to heat transfer being provided via the electrically conductivestructures 112 a (through heating of semiconductor element 112 usingheater 108), it is understood that the heat causing the cleaningreaction of electrically conductive structures 104 a may be provided byan alternative mechanism. For example, a laser source (e.g., a visiblelaser light source, an ultraviolet laser light source, an infrared laserlight source, etc.) may be provided on the bonding machine for heatingelectrically conductive structures 104 a.

Although the invention has been illustrated and described primarily withrespect to a bond head assembly being provided to move the semiconductorelement in order to separate (and re-contact) the electricallyconductive structures of the semiconductor element from the electricallyconductive structures of the substrate, the invention is not limitedthereto. In other examples, the support structure may move the substratein order to separate (and re-contact) the electrically conductivestructures of the semiconductor element from the electrically conductivestructures of the substrate. In other examples, both the bond headassembly and the support structure may move in order to separate (andre-contact) the electrically conductive structures of the semiconductorelement from the electrically conductive structures of the substrate.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

What is claimed:
 1. A method of bonding a semiconductor element to asubstrate, the method comprising the steps of: (a) carrying asemiconductor element with a bonding tool of a bonding machine, thesemiconductor element including a plurality of first electricallyconductive structures; (b) supporting a substrate with a supportstructure of the bonding machine, the substrate including a plurality ofsecond electrically conductive structures; (c) providing a reducing gasin contact with each of the plurality of first electrically conductivestructures and the plurality of second electrically conductivestructures; (d) establishing contact between corresponding ones of theplurality of first electrically conductive structures and the pluralityof second electrically conductive structures after step (c); (e) movingat least one of the semiconductor element and the substrate after step(d) such that the corresponding ones of the plurality of firstelectrically conductive structures and the plurality of secondelectrically conductive structures are separated from one another; (f)re-establishing contact between the corresponding ones of the pluralityof first electrically conductive structures and the plurality of secondelectrically conductive structures after step (e); and (g) bonding thecorresponding ones of the plurality of first electrically conductivestructures to the respective ones of the plurality of secondelectrically conductive structures after step (f).
 2. The method ofclaim 1 wherein the reducing gas includes a carrier gas and an acid. 3.The method of claim 2 wherein the acid includes one of formic acid andacetic acid.
 4. The method of claim 1 wherein the reducing gas is asaturated vapor gas provided via a vapor generation system included onthe bonding machine.
 5. The method of claim 1 wherein, during step (d),heat is transferred from ones of the plurality of first conductivestructures to ones of the plurality of second conductive structures. 6.The method of claim 5 wherein the heat transferred to the ones of theplurality of second conductive structures is provided by a heater of thebonding tool carrying the semiconductor element in step (a).
 7. Themethod of claim 1 wherein a force applied between the corresponding onesof the plurality of first conductive structures and the plurality ofsecond conductive structures during step (d) is less than 10 N.
 8. Themethod of claim 1 wherein a surface of each of the plurality of firstelectrically conductive structures and a surface of each of theplurality of second electrically conductive structures includes areaction product from the reducing gas provided in step (c).
 9. Themethod of claim 8 wherein the reaction product is provided as a resultof (i) a surface oxide on the surface of each of the plurality of firstelectrically conductive structures and the surface of each of theplurality of second electrically conductive structures, and (ii) thereducing gas.
 10. The method of claim 1 wherein additional reducing gasadheres to a surface of each of the plurality of first electricallyconductive structures and a surface of each of the plurality of secondelectrically conductive structures between step (e) and step (f). 11.The method of claim 1 wherein steps (e) and (f) are repeated at leastone time prior to step (g).
 12. The method of claim 1 wherein steps (e)and (f) are repeated a plurality of times prior to step (g).
 13. Themethod of claim 1 wherein step (g) includes applying ultrasonic energybetween the semiconductor element and the substrate.
 14. The method ofclaim 1 wherein step (g) includes bonding the corresponding ones of theplurality of first electrically conductive structures to the respectiveones of the plurality of second electrically conductive structuresthrough a thermocompression bonding process.
 15. The method of claim 1wherein an interface between the ones of the plurality of firstelectrically conductive structures and the respective ones of theplurality of second electrically conductive structures is heated duringthe contact established at step (d).
 16. The method of claim 15 whereinthe interface is heated using a heater of the bonding tool.
 17. Themethod of claim 15 wherein the interface is heated using a heaterseparate from the bonding tool.
 18. The method of claim 17 wherein theheater includes a laser source provided on the bonding machine.
 19. Themethod of claim 1 wherein the bonding tool is carried by a bond head ofthe bonding machine, and wherein step (c) includes providing thereducing gas in contact with each of the plurality of first electricallyconductive structures and the plurality of second electricallyconductive structures via a manifold integrated with the bond head. 20.The method of claim 1 wherein step (c) includes providing the reducinggas in contact with each of the plurality of first electricallyconductive structures and the plurality of second electricallyconductive structures via a manifold integrated with the supportstructure.
 21. A method of bonding a semiconductor element to asubstrate, the method comprising the steps of: (a) carrying asemiconductor element with a bonding tool of a bonding machine, thesemiconductor element including a plurality of first electricallyconductive structures; (b) supporting a substrate with a supportstructure of the bonding machine, the substrate including a plurality ofsecond electrically conductive structures; (c) providing a reducing gasin contact with each of the plurality of first electrically conductivestructures and the plurality of second electrically conductivestructures, the reducing gas being provided via a manifold for directingthe reducing gas to contact each of the plurality of first electricallyconductive structures and the plurality of second electricallyconductive structures, the manifold including a fluid channel forcarrying the reducing gas to an exit portion of the manifold, the fluidchannel being provided along an angle with respect to a horizontal planeof the bonding machine, the angle being between 10-60 degrees; and (d)bonding the corresponding ones of the plurality of first electricallyconductive structures to the respective ones of the plurality of secondelectrically conductive structures after step (c).
 22. The method ofclaim 21 wherein the manifold is integrated with the bond head.
 23. Themethod of claim 21 wherein the manifold is integrated with the supportstructure.
 24. The method of claim 21 wherein, prior to step (d), themethod further comprises the steps of: establishing contact betweencorresponding ones of the plurality of first electrically conductivestructures and the plurality of second electrically conductivestructures after step (c); moving at least one of the semiconductorelement and the substrate after the establishing step such that thecorresponding ones of the plurality of first electrically conductivestructures and the plurality of second electrically conductivestructures are separated from one another; and re-establishing contactbetween the corresponding ones of the plurality of first electricallyconductive structures and the plurality of second electricallyconductive structures after the moving step.